This research is designed to elucidate mechanisms of cellular regulation. The system being investigated is Escherichia coli after infection with bacteriophage T5 or BF23 (a T5-relative). Phage mutants that display altered regulatory patterns have been isolated, and some mutated phage-specific proteins that are involved in regulatory processes have been identified. These regulatory proteins are being isolated so that their mechanisms of action can be tested in cell-free systems. A protein that is responsible for "shutting off" the expression of both host gens an the first group of phage genes to be expressed after infection (pre-early genes) has been partially purified, and is currently being studied in a cell-free transcription system. Both T5 and BF23 modify the membranes of host cells that they infect. Colicinogenic factor Ib, an extra-chromosomal DNA element, also modifies the membranes of cells carrying it, and infection of these Ib-factor containing cells with T5 or BF23 leads to membrane disfunction due probably to over-modification of the cellular membranes. These membrane modifications will be studied from the point of view of protein:protein interactions among host, phage, and Ib-factor specified membrane proteins. BIBLIOGRAPHIC REFERENCES: Lang, D., Shaw, A.R. and McCorquodale, D.J. Molecular Weights of DNA from Bacteriophages T5, T5st(0), BF23 and BF23st(4). J. Virol. 17:296 (1976). Duckworth, D.H., Dunn, G.B. and McCorquodale, D.J. Identification of a Gene Controlling the Synthesis of a Major Membrane protein. J. Virol. in press (1976).